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Philips SGS201
Genre: Enclosed Horizontal Traverse High Pressure Sodium Lantern
As soon as the low pressure sodium lamp (LPS) was developed, the race was on to develop a version which would run at high pressure (HPS).
The research was stimulated by the prospect of the spectral broadening of the light emitted from such a bulb and
the improved colour rendering which would result. However the development was hampered by the lack of a translucent material which
could withstand the chemical attack of sodium vapour at extremely high temperatures and pressures.
It wasn’t until the early 1960s that General Electric (GE) cracked the problems,
closely followed by the GEC and Philips. A prototype high pressure sodium lamp was
exhibited at the APLE's annual conference in 1963, but it wasn’t until 1966 that the GEC erected an experimental installation
along East Lane, Wembley (which, incidentally, also saw the first experimental medium-pressure mercury installation over thirty years before).
The first commercial installation in the UK was erected along the Southend ring road, but it was the City Of London who gained the most
recognition by beginning a radial upgrading of all their lighting to high pressure sodium in 1967. As the early HPS bulbs were designed
to be retrofitted into existing mercury installations, the lanterns chosen by the City Of London were slightly modified versions of
existing mercury lanterns.
The first true HPS lanterns (designed from scratch with the new light source in mind) appeared in the late 1960s and early 1970s. All
these lanterns utilised a cross-over design: whilst this was an adaption of existing mercury lanterns, it also moved the lamp up into
the lantern’s canopy (where it could not be directly viewed by drivers, thus minimalising the glare) and allowed designs to cater for
both cut-off and semi-cut-off.
Wider adoption of high pressure sodium was stalled by the energy crisis, as it couldn’t match the efficiency of its low pressure sodium brother.
Councils, believing in the simple maximum lumens per watt paradigm, replaced existing tungsten, mercury and fluorescent schemes by
low pressure sodium. So it wasn’t until the 1990s that HPS started appearing in greater quantities.
With its efficiency between high pressure mercury and low pressure sodium, HPS became even more attractive when LPS was finally exorcised
from the British Standards of street lighting (as it didn't provide an adequate colour rendering). However, it didn't remain as first choice for
new and replacement lighting schemes for long. Renewed interest in fluorescent (from compact fluorescent sources), the emergence of affordable
metal halide and the possible introduction of LED have all questioned the automatic selection of high pressure sodium for schemes.
Therefore by the end of the first decade of the new century, high pressure sodium’s position as the natural choice for street lighting
was coming under pressure.
Name: Philips SGS201
Date: Early 1970s -
Dimensions: Length: 520mm, Width: 290mm, Depth: 190mm
Light Distibution: Cut-Off
Construction: To BS 4533
Lamp: 35W SOX, 80-125W MBF/U, 50-70W SON
History
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The Philips SGS 201 was introduced amongst a host of new lanterns in mid 1975. Specifically designed
for the newly introduced High Pressure Sodium (HPS) lamp, it was also available in options for high pressure mercury and low
pressure sodium (all of which used the same canopy and gear compartment, but used different gear).
It shared many design traits with its competitors (such as the Thorn Beta 79). The bulb and gear
were housed in two separate compartments, the optics were based on a cross-over reflection system, and the canopy was made from moulded GRP.
Significant differences from other lanterns were the introduction of an entirely curved and figured optical system (whilst the competitor
lanterns used separate side and over reflectors) and an option for either post-top or side entry mounting. (Both these features would
become standard for all lantern types many years later).
The lantern is still being made today and is an important part of the Philips range.
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Popularity
The lantern is extremely popular and can be found installed in many places throughout the UK.
Identification
Owing to its popularity, it is easily identified as it’s so often seen! However, one unique feature is the gear tray
cover which slots over the top of the lantern (and has a dog-legged side which engages with the canopy). Competitor
lanterns of the time had gear trays that unscrewed and swung open from the base of the lantern. (It's designed this way because
the lantern can also be mounted post-top by rotating the spigot, so a hinged lower gear tray isn't an option).
Optical System
A formed polished metal reflector comprises the primary optical system. This totally encases the top half of the
bulb and produces a cross-over flux distribution which results in the cut-off distribution.
Gear
The gear is housed in its own gear compartment. This has a lower IP rating than the lamp compartment and is access
is achieved by unscrewing two screws and lifting the top of the canopy. As access is through the top of the lantern,
no separate gear tray or hinges are required.
The components are screwed into the lantern canopy and include the main lamp choke, a power correction capacitor and an ignitor.
The Philips SGS201 In My Collection
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facing profile
This lantern was originally installed somewhere in Northamptonshire and was obtained from fellow collector Darren.
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front profile
The bowl is held in position by a single stainless steel clip.
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trailing profile
Two characteristics of the lantern can be seen from this angle. The side profile of the bowl is relatively small when compared against
the depth of the canopy; competititor lanterns had much deeper bowls. The gear tray also lifts of from the top of the lantern and
has a distinctive "dog leg" where it turns at 90° to travel along the lip of the canopy.
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canopy
The canopy is smooth and featureless with the exception of a photocell. Another characteristic of the lantern is the spigot
which can be rotated down so the lantern can be fitted as a post-top lantern.
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logo
Unlike many lanterns of their range, Philips chose not to emboss their name and logo on the lantern's canopy.
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pedestrian view
This classic view clearly shows the reflector which encloses the entire upper hemisphere around the bulb. (Competetitor lanterns
often only use two curved side reflectors which a secondary, smaller over-reflector). The spigot assembly can also be clearly
seen where the spigot can be rotated down into a post-top position.
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vertical
The bowl is simply clear and doesn't carry any additional refractors.
Additionally, a small sticker mounted on the base of the gear compartment, gives manufacturer, lantern, bulb and
voltage requirements.
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interior #1
The reflector fills the entire bulb compartment. No light flux emitted above the horizontal is allowed to escape into the
canopy of the lantern.
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interior #2
The gear compartment is small and cramped because a third of the space is required for the spigot assembly. The choke
(a Philips BSN 50L427 ITS for 50W SON lamps) is mounted against one side of the gear compartment wall whilst the
power correction capacitor (a Cambridge Capacitor design rated at 9uF and dated 2005) is mounted above
the ignitor (a Philips SN 67) on the opposite side. There is also space for a terminal block and earth connections.
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Philips SGS201: Night Burning
Philips SGS201: As Aquired
Now becoming a popular lantern on the residental streets of the UK, this 50W SON-T SGS201 was originally installed somewhere on the streets of Northampton.
It was obtained from fellow collector Darren.
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